Digital-to-analog controller-referenced touch sensing system, and related systems, methods, and devices

ABSTRACT

Some disclosed embodiments relate, generally, to shaping a waveform of a reference signal used by a driver of a touch sensor to limit electromagnetic emissions (EME) emitted by a touch sensor during a sensing operation. Some disclosed embodiments relate, generally, to a DAC referenced touch sensor driver and controlling an amount of EME emitted at a touch sensor using shapes of reference signals used by a touch detector to detect touches at the touch sensor. Some disclosed embodiments relate, generally, to compensating for effects of foreign noise at a touch sensor. And more specifically, to changing a shape of a reference signal based on a change to a sampling rate made to compensate for foreign noise.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/379,687, filed Apr. 9, 2019, which claims priority to and the benefitof the filing date of U.S. Provisional Patent Application Ser. No.62/785,141, filed Dec. 26, 2018, the entire contents and disclosure ofeach of which are hereby incorporated herein by this reference.

TECHNICAL FIELD

Systems, methods and devices of the present disclosure relate,generally, to capacitive touch sensing, and more particularly, someembodiments relate to techniques for improved electromagnetic emissionscontrol in touch sensors.

BACKGROUND

A typical touch interface system may incorporate touch sensors (e.g.,capacitive sensors and/or resistive sensors, without limitation) thatrespond to an object in close proximity to, or physical contact with, acontact sensitive surface of a touch interface system. Such responsesmay be captured and interpreted to infer information about the contact,including a location of an object relative to the touch interfacesystem.

Touchpads used with personal computers, including laptop computers andkeyboards for tablets, often incorporate or operate in conjunction witha touch interface system. Displays often include touch screens thatincorporate elements (typically at least a touch sensor) of a touchinterface system to enable a user to interact with a graphical userinterface (GUI) and/or computer applications. Examples of devices thatincorporate a touch display include portable media players, televisions,smart phones, tablet computers, personal computers, and wearables suchas smart watches, just to name a few. Further, control panels forautomobiles, appliances (e.g., an oven, refrigerator or laundry machine)security systems, automatic teller machines (ATMs), residentialenvironmental control systems, and industrial equipment may incorporatetouch interface systems with displays and housings, including to enablebuttons, sliders, wheels, and other touch elements.

While touch sensors emit electromagnetic emissions (EME), such aselectromagnetic fields and electromagnetic radiation, traditionally,designers of touch sensors have been primarily concerned with minimizinga touch sensor's susceptibility to EME from nearby devices. Touchsensors were in the past used in environments where EME limits were veryforgiving. However, limits apply to touch sensors based on theirfunction and the environment in which they are installed. The inventorsof this disclosure appreciate that to meet the strict EME limits of newapplications for touch sensors such as automotive applications,techniques and systems are needed to test, calibrate, and operate touchsensors.

BRIEF DESCRIPTION OF THE DRAWINGS

While this disclosure concludes with claims particularly pointing outand distinctly claiming specific embodiments, various features andadvantages of embodiments within the scope of this disclosure may bemore readily ascertained from the following description when read inconjunction with the accompanying drawings, in which:

FIG. 1 shows a period of an example square waveform;

FIG. 2 shows an example square waveform that is adigital-to-analog-converter (DAC) approximation;

FIG. 3A shows an example edge of a waveform of a signal output from aDAC, where the waveform is monotonic-increasing;

FIG. 3B shows an example edge of a waveform of a signal output from aDAC, where the waveform includes a non-monotonic portion;

FIG. 4 shows a system for configuring a touch sensing system to controlfor EME, in accordance with disclosed embodiments;

FIG. 5 shows an emission control software, in accordance with disclosedembodiments;

FIG. 6 shows a process for configuring a touch sensing system (such astouch sensing system of FIG. 4) to control for EME, in accordance withdisclosed embodiments;

FIG. 7 shows a process for evaluating EME at a touch sensor for aparticular shape of a reference signal, in accordance with disclosedembodiments;

FIG. 8 shows a process for collecting a list of acceptable shapes thatmay be analyzed to determine a shape of a waveform that minimizes EME ata touch sensor, in accordance with disclosed embodiments;

FIG. 9 shows a process for obtaining a cost function, in accordance withdisclosed embodiments;

FIG. 10 shows a touch sensing system configured to provide driverreference signals that are shaped to control for EME emitted by a touchsensor, in accordance with disclosed embodiments;

FIG. 11 shows a process for compensating for foreign noise that utilizesdifferent reference signal shapes, in accordance with disclosedembodiments;

FIG. 12 shows a DAC controller that is configured to change a shape of awaveform of a reference signal responsive to a touch sensing systemchanging a sampling rate (e.g., to compensate for foreign noise by), inaccordance with disclosed embodiment;

FIG. 13 shows an EME control circuitry that is part of or operates inconjunction with a touch sensing system, in accordance with disclosedembodiments; and

FIG. 14 shows a process for dynamically selecting a fundamental andwaveform shape responsive to an application system, in accordance withdisclosed embodiments.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof, and in which are shown,by way of illustration, specific example embodiments in which thepresent disclosure may be practiced. These embodiments are described insufficient detail to enable a person of ordinary skill in the art topractice the present disclosure. However, other embodiments may beutilized, and structural, material, and process changes may be madewithout departing from the scope of the disclosure.

The illustrations presented herein are not meant to be actual views ofany particular method, system, device, or structure, but are merelyidealized representations that are employed to describe the embodimentsof the present disclosure. The drawings presented herein are notnecessarily drawn to scale. Similar structures or components in thevarious drawings may retain the same or similar numbering for theconvenience of the reader; however, the similarity in numbering does notmean that the structures or components are necessarily identical insize, composition, configuration, or any other property.

It will be readily understood that the components of the embodiments asgenerally described herein and illustrated in the drawings may bearranged and designed in a wide variety of different configurations.Thus, the following description of various embodiments is not intendedto limit the scope of the present disclosure, but is merelyrepresentative of various embodiments. While the various aspects of theembodiments may be presented in drawings, the drawings are notnecessarily drawn to scale unless specifically indicated.

The following description may include examples to help enable one ofordinary skill in the art to practice the disclosed embodiments. The useof the terms “exemplary,” “by example,” and “for example,” means thatthe related description is explanatory, and though the scope of thedisclosure is intended to encompass the examples and legal equivalents,the use of such terms is not intended to limit the scope of anembodiment or this disclosure to the specified components, steps,features, functions, or the like.

Thus, specific implementations shown and described are only examples andshould not be construed as the only way to implement the presentdisclosure unless specified otherwise herein. Elements, circuits, andfunctions may be shown in block diagram form in order not to obscure thepresent disclosure in unnecessary detail. Conversely, specificimplementations shown and described are exemplary only and should not beconstrued as the only way to implement the present disclosure unlessspecified otherwise herein. Additionally, block definitions andpartitioning of logic between various blocks is exemplary of a specificimplementation. It will be readily apparent to one of ordinary skill inthe art that the present disclosure may be practiced by numerous otherpartitioning solutions. For the most part, details concerning timingconsiderations and the like have been omitted where such details are notnecessary to obtain a complete understanding of the present disclosureand are within the abilities of persons of ordinary skill in therelevant art.

Information and signals described herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof. Some drawingsmay illustrate signals as a single signal for clarity of presentationand description. It should be understood by a person of ordinary skillin the art that the signal may represent a bus of signals, wherein thebus may have a variety of bit widths and the disclosure may beimplemented on any number of data signals including a single datasignal.

It should be understood that any reference to an element herein using adesignation such as “first,” “second,” and so forth does not limit thequantity or order of those elements, unless such limitation isexplicitly stated. Rather, these designations are used herein as aconvenient method of distinguishing between two or more elements orinstances of an element. Thus, a reference to first and second elementsdoes not mean that only two elements can be employed or that the firstelement must precede the second element in some manner. Also, unlessstated otherwise a set of elements may comprise one or more elements.Likewise, sometimes elements referred to in the singular form may alsoinclude one or more instances of the element.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a special purposeprocessor, a Digital Signal Processor (DSP), an Application SpecificIntegrated Circuit (ASIC), a Field-Programmable Gate Array (FPGA) orother programmable logic device, discrete gate or transistor logic,discrete hardware components, or any combination thereof designed toperform the functions described herein. A general-purpose processor (mayalso be referred to herein as a host processor or simply a host) may bea microprocessor, but in the alternative, the processor may be anyconventional processor, controller, microcontroller, or state machine. Aprocessor may also be implemented as a combination of computing devices,such as a combination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration. A general-purpose computerincluding a processor is considered a special-purpose computer while thegeneral-purpose computer is configured to execute computing instructions(e.g., software code) related to embodiments of the present disclosure.

Also, it is noted that the embodiments may be described in terms of aprocess that is depicted as a flowchart, a flow diagram, a structurediagram, or a block diagram. Although a flowchart may describeoperational acts as a sequential process, many of these acts may beperformed in another sequence, in parallel, or substantiallyconcurrently. In addition, the order of the acts may be re-arranged. Aprocess may correspond to a method, a thread, a function, a procedure, asubroutine, a subprogram, etc. Furthermore, the methods disclosed hereinmay be implemented in hardware, software, or both. If implemented insoftware, the functions may be stored or transmitted as one or moreinstructions or code on computer-readable media. Computer-readable mediaincludes both computer storage media and communication media includingany medium that facilitates transfer of a computer program from oneplace to another.

As understood for purposes of the embodiments described in thisdisclosure, a capacitive sensor may respond to an object's (such as afinger or a stylus) contact with, or the object's proximity to, acontact-sensitive area of the capacitive sensor. In this disclosure“contact” and “touch” are meant to encompass both an object's physicalcontact with a contact-sensitive area and an object's presence withinproximity of a contact-sensitive area without physical contact. Actualphysical contact with a capacitive sensor is not required.

When an object contacts a capacitive sensor, a change in capacitance mayoccur within the touch sensor at or near the location of the contact. Ananalog acquisition front-end may “detect” the touch if it meets acertain threshold. “Charge-then-transfer” is a technique implemented insome touch-acquisition front-ends to detect capacitive changes, wherebya sensing capacitor is charged responsive to the change in capacitance(e.g., charged faster or slower) and the charge is transferred to anintegrating capacitor over multiple charge-transfer cycles. The amountof charge associated with such a charge-transfer may be converted todigital signals by an analog-to-digital converter (ADC), and a digitalcontroller may process those digital signals to determine measurementsand if an object contacted the sensor.

Self-capacitance sensors are capacitive field sensors thatdetect/respond to changes in capacitance to ground. They are typicallylaid out in an array of rows and columns that react independently to atouch. By way of non-limiting example, a self-capacitance sensor mayinclude a circuit employing repetitive charge-then-transfer cycles usingcommon integrated CMOS push-pull driver circuitry having floatingterminals. Mutual capacitance sensors are capacitive field sensors thatdetect/respond to changes in capacitance between two electrodes: a driveelectrode and a sense electrode. The drive electrode and sense electrodepairs at each intersection of drive and sense lines form a capacitor.Self-capacitance and mutual capacitance techniques may be used in thesame touch interface, and complimentary to each other, for example,self-capacitance may be used to confirm a touch detected using a mutualcapacitance.

Touch sensors may be overlaid in a 2-dimensional (2-D) arrangement for a2-D contact sensitive surface that may be incorporated into a contactsensitive surface—for example, of a touch pad or a display screen—andmay facilitate user interaction with an associated appliance. Insulatingprotective layers (e.g., resins, glass, plastic, etc.) may be used tocover touch sensors. As used herein, a “touch display” or “touch panel”is a display (such as a liquid crystal display (LCD),thin-film-transistor (TFT) LCD, or a light emitting diode (LED) display)that incorporates 2-D touch sensors.

Using the example of a touch screen that uses a matrix sensor approachof mutual capacitance sensors employing charge-transfer techniques,drive electrodes may extend in rows on one side of a substrate and senseelectrodes may extend in columns on the other side of the substrate soas to define a “matrix” array of N by M nodes. Each node corresponds toan intersection between the electrically conductive lines of a driveelectrode and of a sense electrode. A drive electrode simultaneouslydrives (i.e., provides an alternating current (A/C) stimulus) all of thenodes in a given row and a sense electrode senses all of the nodes in agiven column. The capacitive coupling of the drive electrode and senseelectrode at a node position may be separately measured or both measuredin response to a capacitive change indicative of a touch event. Forexample, if a drive signal is applied to the drive electrode of row 2and a sense electrode of column 3 is active then the node position is:(row 2, column 3). Nodes may be scanned by sequencing through differentcombinations of drive and sense electrodes. In one mode the driveelectrodes may be driven sequentially while the sense electrodes are allcontinuously monitored. In another mode each sense electrode may besampled sequentially.

Using the example of a touch screen that uses a matrix sensor approachof self-capacitance sensors, electrodes may extend in rows and columnsto define a “matrix” array of N by M nodes. The matrix sensor may beconstructed with an electrode at each node, each electrode beingindividually addressable, or each row and column may be an addressableelectrode and each node corresponds to a unique row/column pair. A drivesignal (i.e., an A/C stimulus) is repeatedly provided to the electrodesof the sensor. When an object contacts the sensor, coupling between theobject and the electrodes increases the current drawn on the electrodeswhich increases the apparent sensor capacitance, and this increase insensor capacitance may be detected. For example, if an increase incapacitance is detected while a drive signal is applied to electrode row2 and electrode column 3, then the location of a touch may be row 2,column 3. Interpolation techniques may be used to identify locationsbetween nodes. Nodes may be scanned sequentially by sequencing throughcombinations of rows and columns of electrodes.

Drive signals (i.e., the AC stimulus) described above is one cause ofEME. Capacitance is typically measured synchronously with the drivesignals. So, there is a direct relationship between the sampling rate ofa measurement and frequency of emission of EME.

Electromagnetic emissions (EME) is meant to broadly include energytransmitted in electromagnetic waves of an electromagnetic field (EMF)that propagates through space (e.g., electromagnetic radiation (EMR)),and [noise] energy transmitted in a current conducted through a material(e.g., conducted emissions).

Emissions measurements is meant to broadly include any measurable valuethat is indicative of EME. Measurement equipment may make use oftechniques for wireless measurements of EME caused by a device (i.e., nophysical connection between measurement equipment and a device),techniques for wired measurements of EME caused by a device (i.e., atleast one physical connection between measurement equipment and adevice, such as a wire), or techniques that use a combination oftechniques for wireless measurements and techniques for wiredmeasurements.

EME of a touch sensor, and more specifically, one or more arrays ofelectrodes that form a touch sensor, can exceed EME limits for certainapplications. As the area of N by M touch sensors increases, so does theEME of the touch sensors. EMR of a touch sensor are the propagating(i.e., radiating) waves of an electromagnetic field (EMF), which wavescarry electromagnetic radiant energy.

Among other things, the waveform of a reference signal used by a driverof a touch sensor may affect the amount of EMR given off by a touchsensor during sensing operation. Sharp transitions from one edge toanother of a waveform create harmonics that increase EMR. FIG. 1 shows aperiod of an example square waveform 1 that includes rising edge 2, topedge 3, falling edge 4, and bottom edge 5. The transitions 6, 7 and 8correspond to increased EMR. FIG. 1 is a simple example. FIG. 2 shows anexample square waveform 10 that is a DAC approximation. The transitionbetween edges as well as the transitions between monotonic portions thatform the edges of square waveform 10 contribute to EMR.

Edges of waveforms can be shaped to control harmonics and therefore theEMR that such harmonics create. A conventional technique for shapingwaveforms in touch sensors is to use passive filters, but using specifichardware ties each touch sensor to a specific solution that may not meetEME limits for different applications or meet limits for the sameapplication but in different countries. For example, a touch sensor withpassive filters used in an application with radio frequency (RF)antennas nearby in Europe may not meet the EME limits for the sameapplication in the United States, nor might it meet EME limits for anapplication with RF antennas using different frequency bands.

Moreover, there is a trade-off in sensing speed when passive filters areused to shape waveforms of driver reference signals. Sensing speed ishow quickly a touch processor can identify contact with a touch sensor.Sensing speed is affected by acquisition rate, which is how often atouch processor can measure the capacitance on the electrodes of a touchsensor (acquisition rate is also referred to herein as “sampling rate”).The higher the acquisition rate the faster the sensing speed. Bestacquisition rates are achieved when a driver reference signal has a flattop, but passive filters provide signals with a waveform that has adownward sloping top—not a flat top.

Finally, passive filtering techniques known to the inventors of thisdisclosure do not compensate for the non-linearities in the touch sensordrivers.

So, the inventors of this disclosure appreciate a need for waveformshaping techniques without some or all of the disadvantages of passivefiltering techniques.

Non-monotonic portions of a waveform can be used to control harmonicsand therefore EMR of a driver reference signal. FIG. 3A, shows anexample edge 12 of a DAC outputted waveform, where the edge 12 may becharacterized as monotonic-increasing. FIG. 3B shows an example edge 13of a DAC outputted waveform, where the edge 13 includes a portion 14that may be characterized as non-monotonic, and so edge 13 is alsocharacterizable as non-monotonic. In this disclosure, waveforms thathave intentionally introduced non-monotonic portions are referred to as“arbitrary waveforms” and the signals that have such waveforms arereferred to as “arbitrary signals.”

There is a need for waveform shaping techniques that can be used tocreate arbitrary waveforms for a reference signal of a touch sensordriver in order to control harmonics, and to control EME more generally.

Some disclosed embodiments relate, generally, to shaping a waveform of areference signal used by a driver of a touch sensor to limit EME emittedby a touch sensor during a sensing operation. In disclosed embodiments,shaping may be performed for one or more frequency bands of samplingfrequencies usable for sensing operations. Shaping may be performed on aportion of a waveform of a reference signal or on an entire waveform.One or more shapes may be selected that are detected to correspond toEME below a pre-defined limit (or within a pre-defined range) for one ormore frequency bands. N-bit digital codes (also referred to herein as“n-bit codes”) may be stored that correspond to selected shapes. In someembodiments, selected shapes may be arbitrary shapes. In someembodiments, selected shapes may include non-monotonic and/or monotonicportions and at least some n-bit codes of sequences of n-bit codes maycorrespond such portions.

It should be appreciated that disclosed embodiments have many advantagesand benefits, including but not limited to those described herein. Forexample, in some disclosed embodiments, electromagnetic radiationcaused, at least in part, by known and unknown non-linearities of DACsusable to generate reference voltages for drivers may be overcome.

In disclosed embodiments, a shape of a waveform (i.e., a “waveformshape”) of a driver reference signal may be described in terms of ashape of the waveform of a driver reference signal output by a DACand/or a sequence of n-bit codes applied to a DAC to generate a signalhaving such a shape.

FIG. 4 shows an embodiment of a system 100 for configuring a touchsensing system 110 to control for EME. System 100 may include touchsensing system 110, touch sensor 130, measurement equipment 140,emission control software 150, and emission requirements 160. Touchsensing system 110 is configured, generally, to measure capacitances attouch sensor 130 and detect and report touches responsive to thosemeasurements.

Touch sensing system 110 may include DAC referenced drivers 111 and 112,n-bit DACs 113 and 114, DAC control 115, and touch detector 116. N-bitDACs 113 and 114 are configured to receive bit-streams 117 and 118,respectively, and output driver reference signals 119 and 120,respectively, responsive to the bit-streams 117 and 118. In the exampleshown in FIG. 4, reference signals 119 and 120 are labeled as outputreference 119 and input reference 120 because this example uses separatedrivers for rows and columns of electrodes of touch sensor 130. In otherembodiments different numbers of drivers may be used than in thisexample, including one driver or more than two drivers.

DAC control 115 is configured to provide bit-streams 117 and 118 ton-bit DACs 113 and 114, respectively. In disclosed embodiments,bit-streams 117 and 118 correspond to signal shapes. DAC control 115 maystore bit-streams of signal shapes in memory (not shown). For example,if using a 4-bit DAC, then DAC control 115 stores a sequence of 4-bitcodes and that sequence of 4-bit codes corresponds to a waveform havinga desired shape. DAC control 115 may store a first sequence of n-bitcodes to cause n-bit DAC 113 to generate reference signal 119, and storea second sequence of n-bit codes to cause n-bit DAC 114 to generatereference signals 120.

In the example shown in FIG. 4, DAC control 115 controls both n-bit DACs113 and 114. In another embodiment, touch sensing system 110 may includemultiple DAC control modules, for example, each n-bit DAC may becontrolled (i.e., receive a bit-stream) from a dedicated DAC controlmodule.

Measurement equipment 140 is configured, generally, to measure EME 132emitted from touch sensor 130. More specifically, measurement equipment140 is configured to measure EME 132 emitted from touch sensor 130during sensing operations and to provide emissions measurements 142corresponding to EME 132 during sensing operations to emission controlsoftware 150. Measurement equipment 140 may include any suitablesensor(s) for directly or indirectly measuring EME 132, for example,spectrum analyzers, Gauss meters, EMF meters, multimeters for measuringbody voltage, E-field sensors, and/or H-field sensors. Emission controlsoftware 150 is configured, generally, to analyze emissions measurements142 corresponding to a sensing operation and based on those results,evaluate the sequence of n-bit codes and therefore the shape of thedriver reference signals 119 and 120 used during the sensing operation.For example, emission control software 150 may evaluate a sequence ofn-bit codes by comparing emissions measurements 142 to applicable EMErequirements 160. If emissions measurements 142 are below the applicablelimits, then the sequence of n-bit codes may be stored by DAC control115. If emissions measurements 142 exceed the applicable limits, thenthe emission control software 150 may provide a new sequence of n-bitcodes for a new signal shape to DAC control 115 for testing. The processof selecting a sequence of n-bit codes, performing sensing operations,measuring EME 132, and evaluating the sequence of n-bit codes based onmeasured EME 132 and emissions requirements 160, may be repeated untilan acceptable signal shape is identified.

Emissions requirements 160 may include standards 162 and/or customrequirements 164. By way of example, standards 162 may be an automotivestandard such as CISPR25 which is a standard for controllingelectromagnetic interference in electrical and electronic devices usedin automotive applications. Custom requirements 164 may be anything,including for example customer requirements, requirements that exceedstandards, and requirements for applications where there are nostandards or no industry-accepted standards.

FIG. 5 shows an embodiment of emission control software 150 thatincludes waveform optimizer 152, code generator 154, and emissionsanalyzer 156. Waveform optimizer 152 is configured, generally, todetermine changes to a shape of a waveform to, in theory, improve EMEemitted from touch sensor 130 during a sensing operation. In oneembodiment, waveform optimizer 152 may select changes based on anoptimization algorithm, and more specifically, according to an output ofa cost function as described more fully, below. It should be understoodthat disclosed embodiments do not require that an actual change in shapeof a waveform determined by waveform optimizer 152 actually be optimal.

Code generator 154 is configured, generally, to generate a sequence ofn-bit codes that correspond to the shapes of the waveforms selected bywaveform optimizer 152. Emissions analyzer 156 is configured, generally,to analyze the emissions measurements 142 from measurement equipment 140and determine how EME emitted from touch sensor 130 compares to variousemissions requirements.

In disclosed embodiments, any suitable global optimization algorithm maybe used to find a waveform shape that improves EME. In one embodiment,each sequence of n-bit codes that are tested is a parameter for a globaloptimization algorithm. In some cases a list of sequences of n-bit codesmay be long and so an optimization algorithm may wander for an excessiveperiod of time, so in one embodiment, a smaller number of parameters maybe used to represent a waveform in addition to, or as an alternative to,using a list of sequences of n-bit codes. For example, a waveform may berepresented as a polynomial evaluated at different instants, and theparameters for the global optimization algorithm are the coefficients ofthe polynomial at a given instant. By way of another example, a waveformmay be represented as splines, Bezier curves, or coefficients of aTaylor series, which allows complex shapes to be represented with alimited list of parameters.

FIG. 6 shows a process 200 for configuring a touch sensing system (suchas touch sensing system 110) to control for EME, in accordance withdisclosed embodiments. In operation 201, reference signals are providedto a driver during a number of sensing operations. Each of the referencesignals provided during different sensing operations has a differentshape. In other words, a reference signal provided during a firstsensing operation has a different shape than a reference signal providedduring a subsequent sensing operation. In operation 202, an optimalshape for a reference signal is detected responsive to EME emitted by atouch sensor while providing the reference signals. In one embodiment,an optimal shape for a reference signal may be detected because it isthe first shape that is below an applicable EME limit. In anotherembodiment, an optimal shape for a reference signal may be detectedbecause it corresponds to the lowest EME measurement of a number ofshapes that were tested (i.e., the shape corresponds to a minimum EMEmeasurement). In one embodiment, an optimal shape for a reference signalmay be detected because it corresponds to the lowest EME measurement ofa number of shapes that were tested that were below an EME limit. Inoperation 203, instructions are stored for causing a DAC to generate areference signal having the optimal shape. The instructions may be orinclude sequences of n-bit codes that correspond to the optimal shape.

FIG. 7 shows a process 210 for evaluating EME at a touch sensor for aparticular shape of a reference signal, in accordance with disclosedembodiments. In operation 211, a driver reference signal is provided fora sensing operation, the reference signal having a pre-selected shape.In operation 212, EME emitted by a touch sensor during the sensingoperation is measured. In operation 213, if EME is acceptable becausethe EME measurements are below applicable limits, then in operation 216the sequence of n-bit codes corresponding to the current shape ofreference signal is stored and process 210 ends. If not acceptable, inoperation 214, a new shape for a reference signal is selected responsiveto the measured EME, and in operation 215, a new reference signal for adriver is provided having the new shape, and operation 212 is againperformed.

FIG. 8 shows a process 220 for collecting a list of acceptable signalshapes that may be analyzed to determine the signal shape that improvesEME at a touch sensor, in accordance with disclosed embodiments. Inoperation 221, a driver reference signal is provided for a sensingoperation, the reference signal having a pre-selected signal shape. Inoperation 222, EME emitted by a touch sensor during the sensingoperation is measured. In operation 223, if EME is acceptable becausethe EME measurements are below applicable limits, then in operation 227the sequence of n-bit codes corresponding to the current shape ofreference signal is stored.

In operation 224, a determination is made whether there are more signalshapes to test, and if not, then process 220 ends. In one embodiment,the tested signal shapes may be a set of pre-selected signal shapes andprocess 220 ends if all the pre-selected signal shapes have been tested.

In another embodiment, a cost function may be used, and process 220 endswhen a shape that minimizes the cost function is found. A cost functionmay analyze an emission measurement and return an output which valuescompliance of EME against an emissions requirements.

If more signal shapes should be tested, then in operation 225, a newsignal shape for a reference signal is selected, and in operation 226, anew reference signal for a driver is provided having the new signalshape. If there are multiple sequences of n-bit codes stored, then asequence of n-bit codes that has the lowest EME may be selected.

FIG. 9 shows a flow chart of a process 230 for obtaining a cost functionsuch as a cost function used in process 220, in accordance withdisclosed embodiments. In embodiments of FIG. 9, a cost function mayreturn a lower value to represent improving compliance with an emissionsrequirement and return a higher value to represent worsening compliancewith an emissions requirement. In other embodiments, other conventionsmay be used.

In operation 231, a number of emissions measurements are received. Theemissions measurements may correspond to a particular waveform shape. Inoperation 232, a highest emissions measurement of the emissionsmeasurement is identified. The highest emissions measurement may beidentified notwithstanding it being above or below a defined emissionslimit.

In operation 233, excess values are obtained and stored. For each of theexcess values, an excess value may be obtained by calculating adifference between each emission measurement of operation 231 and adefined emission limit.

In operation 234, a margin value is obtained and stored. The marginvalue may be obtained by calculating a difference between the highestemissions measurement identified in operation 232 and the definedemissions limit. In operation 235, the excess values are summed and thesummed excess values are used to increase the cost function. If thereare no excess values, then in operation 236, the margin value is used todecrease the cost function.

Other embodiments may additionally or alternatively obtain a costfunction by subtracting the margin value from the summed excess values,and using the result to either increase or decrease the cost function(depending on if the result is positive or negative).

In some embodiments, an emissions requirement may define emission limitsin several frequency bands and a process such as process 230 may be usedto determine a cost function associated with a waveform shape for eachof the frequency bands. In other embodiments, an emissions requirementmay define several frequency bands and for each frequency band defineemission limits for different measurement methodologies, and processsuch as process 230 may be used to determine a cost function associatedwith a waveform shape for each combination frequency band andmeasurement methodology. For example, an emissions requirement maydivide a spectrum into an RFID band, a long wave (LW) band, and a mediumwave (MW) band; and for each frequency band define emission limits forpeak (PK), quasi peak (QP), and/or average (AV) emissions. So, for eachcombination of frequency band of interest and measurement methodology, acost function may be determined.

In some embodiments, a configuration process (such as processes 200, 210and 220) may be performed multiple times for different sampling ratesthat have different fundamental frequencies. Multiple sequences of n-bitcodes may be stored, where each sequence of n-bit codes is associatedwith a signal shape that optimizes EME for a particular samplingrate/fundamental frequency. Some advantages of storing multiplesequences of n-bit codes for different fundamental frequencies aredescribed with reference to FIGS. 10 and 11.

Some disclosed embodiments relate, generally, to a DAC referenced touchsensor driver and controlling an amount of EME emitted at a touchsensor. More specifically, a DAC is controlled to generate a shapedreference signal that has a waveform shaped to control an amount of EMEemitted at a touch sensor to meet EME limits. Such limits may be, forexample, defined by standard or customized for a particular applicationin which a touch sensing system is used.

FIG. 10 shows an embodiment of a touch sensing system 300 configured toprovide reference signals 306 and 307 that are shaped to control EMEemitted by a touch sensor according to disclosed embodiments. In theexample shown in FIG. 10, touch sensing system 300 is configured,generally, to perform self-capacitance sensing techniques. Touch sensingsystem 300 may include drivers 301 and 302, n-bit DACs 303 and 304, andtouch detector 305. Touch controller 310 has stored n-bit codes 311 thatcorrespond to improved shapes for reference signals 306 and 307.Bit-stream generator 312 is the logic that enables DAC controller 310 togenerate bit-streams 308 and 309 that cause n-bit DACs 303 and 304 tooutput reference signals having improved shapes, in cooperation with areceived clock signal. More specifically, bit-stream generator 312 maycontrol the rate at which bit-streams 308 and 309 are provided to n-bitDACs 303 and 304 based on, for example, a desired sampling rate used bytouch sensing system 300. Drivers 301 and 302 may output drive signals315 and 316 for driving electrodes of a touch sensor (not shown),respectively, responsive to reference signals 306 and 307, respectively.

Touch detector 305 is configured to measure 313 signal levels of drivesignal 316 and detect changes in the signal level caused by contact at atouch sensor operatively coupled to touch sensing system 300. Morespecifically, touch detector 305 may detect an increase in the currentcause by apparent additional capacitance from an object contacting atouch sensor. Touch detector 305 reports a touch 314 if it detects achange in the signal level that meets or exceeds a threshold.

While, in the example system shown in FIG. 10, touch detector 305 isshown measuring 313 drive signal 316, disclosed embodiments are not solimited. Touch detector 305 may also measure 313 drive signal 315 todetect a touch, or measure 313 both drive signal 315 and drive signal316 to detect a touch. While the example system shown in FIG. 10includes two drivers 301 and 302, it should be appreciated that othernumbers of drivers may be used to provide drive signals to a touchsensor, for example, one driver or more than two drivers. While theexample system shown in FIG. 10 is configured to performself-capacitance sensing techniques, and contemplated operationsdescribed herein have been described with reference to self-capacitancesensing, disclosed embodiments are not so limited. In anotherembodiment, touch sensing system 300 may be configured for mutualcapacitive sensing, where drive signals and sense signals are providedto a touch sensor responsive to shaped reference signals, and touchdetector 305 is configured to measure sense signals to detect touches atthe touch sensor.

In some cases, a frequency of a sampling rate may cause a measurement tobe susceptible to foreign noise, but a different frequency may not causea measurement to be susceptible or as susceptible to the foreign noise.Some disclosed embodiments relate, generally, to compensating foreffects of foreign noise at a touch sensor. In disclosed embodiments, asampling rate may be changed from a first sampling rate to a secondsampling rate responsive to foreign noise. More specifically, indisclosed embodiments, a sampling rate may be changed to a secondsampling rate that is less susceptible (i.e., influenced by) the foreignnoise than the first sampling rate. The first sampling rate may beassociated with a first fundamental frequency and the second samplingrate may be associated with a second fundamental frequency. A shape of areference signal usable by a driver may be changed responsive to thesecond fundamental frequency.

FIG. 11 shows an embodiment of a process 320 for compensating forforeign noise that utilizes different reference signal shapes. Inoperation 321, a first driver reference signal is output. The driverreference signal has a first shape which it corresponds to a firstfundamental frequency for a first sampling rate. In operation 322 atouch sensor is measured at the first sampling rate, which is associatedwith the first fundamental frequency. In operation 323, a secondfundamental frequency is determined responsive to a detectedinterference. In one embodiment, a second sampling rate is determinedthat reduces susceptibility to the foreign noise and the secondfundamental frequency is determined based on the second sampling rate.In one embodiment, the second fundamental frequency and second samplingrate may be one of a number of predetermined fundamental frequencies andpredetermined sampling rates, respectively, that have a predeterminedassociation. In operation 324, a second reference signal for a driver isprovided. The second reference signal has a second shape, different thanthe first shape, and the second shape is associated with the secondfundamental frequency. In operation 325, the touch sensor is sampled ata second sampling rate, which is associated with the first fundamentalfrequency.

FIG. 12 shows an embodiment of a DAC controller 400 that is configuredto change the shape of a reference signal responsive to a touch sensingsystem changing a sampling rate (e.g., to compensate for foreign noise).DAC controller 400 includes a processor 401, a program memory 402 and adata memory 406 (the data memory 406 could just be part of the programmemory depending on the implementation). Program memory 402 isconfigured to store programs for various applications related toperforming disclosed embodiments, including controlling a DAC to changethe shape of a reference signal. In this example, code selector 403,fundamental frequency detection 404, and bit-stream generator 405 arestored at program memory 402. Data memory 406 is configured to storesequences of n-bit codes 407 for improved shapes of reference signals.Each stored sequence of n-bit codes 407 is associated with a particularfundamental frequency, f₀, 408. In one embodiment, the sequences ofn-bit codes 407 and fundamental frequencies 408 may be stored as alook-up-table (LUT), and the LUT may be searchable using values for thefundamental frequencies 408, sampling rates corresponding to thefundamental frequencies f₀, or some other key.

In a contemplated operation of DAC controller 400, fundamental frequencydetection 404 determines that a sampling rate has changed for example,because bit-stream generator 405 has changed the bit-stream rate toaccommodate a new sampling rate. Fundamental frequency detection 404determines a fundamental frequency associated with the new samplingrate. Code selector 403 uses the fundamental frequency to select asequence of n-bit codes from among sequences of n-bit codes 407 storedon data memory 406. In another embodiment, code selector 403 may use anew sampling rate determined based on the bit stream rate of thebit-stream generator 405 (in which case the fundamental frequencydetection 404 may be omitted). Code selector 403 provides the selectedsequence of n-bit codes to bit-stream generator 405 to generate thebit-streams for the DACs.

For some applications, EME requirements may be so stringent that not allEME limits may be met by a single fundamental frequency and waveformshape. Stated another way, multiple EME limits may be associated with acertain application, and no single fundamental frequency and waveformshape combination may be found that does not result in undesirableharmonics—i.e., harmonics that cause a touch system to exceed at leastone of the EME limits.

For example, in a contemplated application, EME limits may be enforcedfor RFID, LW and MW bands. A touch system operating with a givenfundamental frequency and waveform shape may be able to respect (i.e.,meet) EME limits for RFID and LW, but exceeds EME limits for MW.Alternatively, the touch system using a different fundamental andwaveform shape or the same fundamental and a different waveform shapemay be able to respect EME limits for RFID and MW, but exceed EME limitsfor LW. In other words, in this example, a fundamental and shape isfound that would satisfy EME limits for RFID and LW; a fundamental andshape is found that would satisfy EME limits for RFID and MW; but nofundamental and shape is found that would satisfy EME limits for RFID,MW, and LW.

So, some disclosed embodiments relate, generally, to an emissionscontrol circuitry, and a touch sensing systems including the same, thatis configured to perform dynamic selection of touch sensing fundamentalfrequency and/or waveform shape for a touch sensing system based, atleast in part, on system-level use information and qualitative EMEinformation. System level use information may be, for example,information about a current state of other devices in an applicationsystem of which a touch sensing system is a part, or system-level useinformation may be instructions about how to prioritize EME limits(e.g., prioritize MW limits over LW limits).

Qualitative EME information is qualitative characterizations ofassociated fundamental frequencies and waveform shapes and/orinformation that could be used to characterize, qualitatively,associations of fundamental frequencies and waveform shapes—in terms ofEME. Qualitative EME information may include for various pairs offundamental and waveform shape, for example, information aboutharmonics, information about EME limits for specific bands and/orregions, information about whether specific EME limits are satisfied orhave been tested, or any other information that could be used todetermine whether EME limits relevant to an application system could bemet by a given fundamental and waveform shape. Satisfied EME limits maybe expressed, for example, as EME levels that might result duringoperation, satisfied portions of the spectrum (e.g., LW, MW, and RFID),and satisfied limits for specific geographic region (e.g., NorthAmerica, South America, and Europe). Information about satisfied EMElimits may also include information about EME limits that are notsatisfied, broken down, for example, by geographic region or bands.

FIG. 13 shows an EME control circuitry 505 that is part of or operatesin conjunction with a touch sensing system 502, in accordance withdisclosed embodiments. In disclosed embodiments, touch sensing system502 may include touch detection circuitry 503, touch sensing circuitry504, and EME control circuitry 505; and is part of touch system 500 thatalso includes touch sensor 501. In the embodiment shown in FIG. 13,touch system 500 is a sub-system that is part of a more encompassingapplication system that may include other devices and/or components (notshown). Touch sensing circuitry 504 may be configured to provide andreceive sensing signals 512 (e.g., drive signals) to touch sensor 501,and touch detection circuitry 503 may be configured to report touches513 responsive to measurements 511 based on sensing signals 512.

In disclosed embodiments, EME control circuitry 505 may be configured,generally, to monitor a state of an application system and controloperation of touch sensing circuitry 504 in order to meet certain EMErequirements. EME control circuitry 505 may be configured to store(e.g., in data memory, registers, a buffer, and combinations thereof)state information 508 about a broader application system and qualitativeEME information 507 about improved fundamentals and associated waveformshapes, select fundamentals and/or waveform shapes based, at least inpart, on stored state information 508 and qualitative EME information507, and provide selection signals 510 responsive to the selectedfundamentals and/or waveforms.

In one embodiment, EME control circuitry 505 may be configured toreceive system-level use information 509 about an application system andstore state information 508 based, at least in part, on the receivedsystem-level use information 509. In one embodiment, an applicationsystem may provide system-level use information 509 to touch system 500.For example, an application system may provide as system-level useinformation 509: information about other devices in the system,information about EME limits associated with those devices, and/orinformation about application specific settings, such as region settings(e.g., North America, South America, or Europe). In one embodiment, EMEcontrol circuitry 505, touch sensing system 502, or touch system 500more generally, may include a communications link or communicationsprotocol to collect or receive system-level use information 509 from anapplication system, for example, from a computer, sub-system, or stackof the application system.

For example, if an application system includes multiple radiotransmitters and receivers, system-level use information 509 may includeinformation about which bands and/or frequencies the radios areconfigured to receive/transmit and/or which bands and/or frequencies areactually being received/transmitted by the radios.

In the embodiment shown in FIG. 13, fundamentals and associated waveformshapes (e.g., sequences of n-bit code) may be stored with qualitativeEME information 507 or in another memory location (not shown) accessibleby selection logic 506. Indeed, in the embodiment shown in FIG. 13, EMEcontrol circuitry 505 may be, or be part of, a DAC controller (such asDAC controller 310 shown in FIG. 10) for controlling a DAC (not shown,but such as DAC 303 or 304 of FIG. 10), and selection signals 510 maybe, e.g., driver reference signals. In another embodiment, EME controlcircuitry 505 may be a separate module (i.e., separate from a DACcontroller) and configured to provide selection signals 510 to a DACcontroller that is part of touch sensing circuitry 504. For example, EMEcontrol circuitry 505 may be configured to provide information to a DACcontroller about a selected fundamental and shape having favorable EMEcharacteristics, and such DAC controller may then select a sequence ofn-bit codes that corresponds to the information provided by EME controlcircuitry 505.

EME control circuitry 505 may include fundamental and waveform shapeselection logic 506 configured to dynamically select a fundamental andwaveform shape based, at least in part, on state information 508 andqualitative EME information 507. In one embodiment, fundamental andwaveform shape selection logic 506 may be configured to monitor thestate information 508 and detect changes to state information 508. Iffundamental and waveform shape selection logic 506 detects a change,then fundamental and waveform shape selection logic 506 may beconfigured to select a fundamental and waveform shape based onqualitative information 507 and new state information 508 and provideselection signals 510 responsive to the selection.

FIG. 14 shows an embodiment of a process 520 for dynamically selecting afundamental and waveform shape responsive to an application system.

In operation 521, a first sensing signals are provided responsive to afirst reference signal. The first reference signal may have a shapecorresponding to a first waveform shape associated with a firstfundamental frequency. The first fundamental frequency and firstwaveform shape may have favorable EME characteristics for an applicationsystem as set forth in qualitative EME information characterizing theassociation of the first fundamental frequency and the first waveform.In operation 522, a touch sensing measurement is performed responsive tothe first sensing signals. In one embodiment, the first sensing signalsare drive signals and the touch sensing measurement is aself-capacitance measurement. In operation 523, new state informationabout the application system is detected. In operation 524, a secondfundamental frequency and/or a second waveform shape are selectedresponsive to the new state information and qualitative EME informationthat characterizes associations of a number of pairs of fundamentalsfrequencies and waveform shapes including those selected. The secondfundamental frequency and/or second waveform shape may be selected, forexample, because qualitative EME information characterizes anassociation more favorably in terms of EME given the new stateinformation than the first fundamental frequency and the first waveformshape (and preferably more favorably than other combinations offundamental frequencies and waveform shapes that are available). Themore favorable EME characteristics may be, for example, indications thatfundamental frequencies and associated wave form shapes result in EMEwithin EME limits for various devices within the application system orwithin a geographic regions where the application system is deployed.

In operation 525, a second reference signal is provided. The secondreference signal has a second waveform shape, different than the firstwaveform shape. In operation 526, a second sensing signal is providedresponsive to the second reference signal and, in operation 527, a touchsensor measurement is performed responsive to the second sensingsignals.

One having ordinary skill in the art would understand that disclosedembodiments have many advantages and benefits. For example, enablingcompliance with different electromagnetic emission limits based on alocation of a radio antenna, based on a radio quality, based on alocation of use (e.g., a country that has specific requirements relatedto EME, without limitation), and/or based on a presence of otherequipment (e.g., audio system, remote entry equipment for an automobile,communication equipment, without limitation); enabling compliance withEME requirements for radio band (e.g., frequency band, withoutlimitation) allocations world-wide; and the ability to control spectralcontent by software without using hardware passive filters.

By way of further example, disclosed embodiments enable adjustment of aDAC controller and a touch sensing system more generally, aftermanufacture and so may accelerate time to market by saving redesigncycles that are otherwise required for systems that use passive filters.

By way of yet further example, combining a DAC solution with tuningsoftware (e.g., emission control software 150) may compensate fornon-linearities in a driver stage that would otherwise cause signals atunwanted harmonics.

By way of yet further example, using software to control a DAC togenerate shaped reference signals for a driver enables faster signalacquisition than other solutions such as hardware passive filters.

While the present disclosure has been described herein with respect tocertain illustrated embodiments, those of ordinary skill in the art willrecognize and appreciate that the present invention is not so limited.Rather, many additions, deletions, and modifications to the illustratedand described embodiments may be made without departing from the scopeof the invention as hereinafter claimed along with their legalequivalents. In addition, features from one embodiment may be combinedwith features of another embodiment while still being encompassed withinthe scope of the invention as contemplated by the inventor(s).

Additional non-limiting embodiments of the disclosure include:

Embodiment 1: A touch sensing system, comprising: adigital-to-analog-converter (DAC) controller configured to output a codefor a waveform shape, wherein the code or the waveform shape isassociated with exhibiting electromagnetic emissions (EME) at the touchsensing system below a limit; a DAC configured to output a first shapedreference signal responsive to the code output by the DAC controller; adriver configured to provide a drive signal for a touch sensorresponsive to the first shaped reference signal; and a touch detectorconfigured to report touches responsive to a changed signal level of thedrive signal.

Embodiment 2: The system according to Embodiment 1, wherein the DACcontroller is configured to store sequences of n-bit codes, and whereinthe code for the waveform shape output by the DAC controller is abitstream comprising one of the stored sequences of n-bit codes.

Embodiment 3: The system according to any of Embodiments 1 and 2,wherein at least one other of the stored sequences of n-bit codes isassociated with exhibiting EME at the touch sensing system below adifferent limit.

Embodiment 4: The system according to any of Embodiments 1 through 3,wherein the DAC controller is configured to store sequences of n-bitcodes, and each of the stored sequences of n-bit codes is associatedwith different sampling rates.

Embodiment 5: The system according to any of Embodiments 1 through 4,wherein the DAC controller is configured to output a first code for afirst waveform shape responsive to a first fundamental frequency and tooutput a second code for a second waveform shape responsive to a secondfundamental frequency, wherein the first fundamental frequency isassociated with a first sampling rate and the second fundamentalfrequency is associated with a second sampling rate.

Embodiment 6: The system according to any of Embodiments 1 through 5,wherein the DAC controller is configured to: provide a first bit streambased, at least in part, on a first sequence of n-bit codescorresponding to a shape of the first shaped reference signal; andprovide a second bit stream based, at least in part, on a secondsequence of n-bit codes corresponding to a shape of a second shapedreference signal.

Embodiment 7: The system according to any of Embodiments 1 through 6,wherein the DAC controller is configured to provide the first bit streamat a first rate associated with a first sampling rate, and provide thesecond bit stream at a second rate associated with a second samplingrate.

Embodiment 8: The system according to any of Embodiments 1 through 7,further comprising one or more memories, the one or more memoriesconfigured to store: sequences of n-bit codes for waveform shapes;qualitative electromagnetic emissions (EME) information characterizingassociations of fundamentals and at least some of the sequences of n-bitcodes; and state information about an application system.

Embodiment 9: The system according to any of Embodiments 1 through 8,wherein a first sequence of n-bit codes and a second sequence of n-bitcodes are associated with the same fundamental frequency, and whereinthe qualitative EME information comprises: a first characterization ofharmonics of the fundamental frequency and first sequence of n-bitcodes; and a second characterization of harmonics of the fundamentalfrequency and the second sequence of n-bit codes.

Embodiment 10: The system according to any of Embodiments 1 through 9,further comprising selection logic configured to select a sequence ofn-bit codes of the sequences of n-bit codes responsive to the stateinformation and the qualitative EME information.

Embodiment 11: A touch sensing method, comprising: providing a firstcode for a waveform shape for a digital-to-analog converter (DAC),wherein the first code or the waveform shape is associated withelectromagnetic emissions (EME) at a touch sensing system below a limit;providing a first shaped reference signal for a driver responsive to thefirst code for the waveform shape; providing a drive signal for a touchsensor responsive to the first shaped reference signal; and reporting atouch responsive to a changed signal level of the drive signal.

Embodiment 12: The method according to Embodiment 11, wherein providingthe first code for the waveform shape comprises providing a bitstreamcomprising a sequence of n-bit codes.

Embodiment 13: The method according to any of Embodiments 11 and 12,further comprising: measuring the drive signal at a first sampling rate;providing a second code for a waveform shape for the DAC responsive todetecting that a sampling rate has changed from a first sampling rate toa second sampling rate; providing a second reference signal for thedriver responsive to the second code for the second waveform shape;providing a second drive signal for the touch sensor responsive to thesecond reference signal; and measuring the second drive signal at thesecond sampling rate.

Embodiment 14: The method according to any of Embodiments 11 through 13,wherein the second sampling rate is associated with less susceptibilityto foreign noise than the first sampling rate.

Embodiment 15: The method according to any of Embodiments 11 through 14,further comprising: providing a first bitstream of the first code forthe first waveform shape at a first rate associated with the firstsampling rate; and providing a second bitstream of the second code forthe second waveform shape at a second rate associated with the secondsampling rate.

Embodiment 16: The method according to any of Embodiments 11 through 15,comprising: performing a first touch measurement responsive to theproviding the drive signal;

providing a second code for a second waveform shape for the DACresponsive to detecting that state information for an application systemhas changed; providing a second shaped reference signal for the driverresponsive to the second code for the second waveform shape; providing asecond drive signal for the touch sensor responsive to the secondreference signal; and performing a second touch measurement responsiveto providing the second drive signal.

Embodiment 17: The method according to any of Embodiments 11 through 16,further comprising determining that a harmonic associated with thesecond waveform shape has more favorable electromagnetic emissions (EME)characteristics responsive to the changed state information about theapplication system and qualitative EME information about harmonicsassociated with the second waveform shape.

Embodiment 18: A system for configuring a touch sensing system tocontrol for electromagnetic emissions (EME), the system comprising: atouch sensing system configured to detect touches at a touch sensorresponsive to sensed signals; and emissions control software that, whenexecuted by a processor, is configured to: receive EME measurementsobtained responsive to EME emitted by the touch sensor during a sensingoperation; evaluate a shape of a reference signal used by the touchsensing system to detect the touches at the touch sensor responsive tothe EME measurements and one or more emissions requirements; andconfigure the touch sensing system to use an improved shape for thereference signal used to detect touches, the improved shapecorresponding to the EME measurements that is below the one or moreemissions requirements.

Embodiment 19: The system according to Embodiment 18, wherein the shapeof the improved shape is characterized by one or more of a substantiallyflat top edge, a rising edge having one or more non-monotonic portions,and a falling edge having one or more non-monotonic portions.

Embodiment 20: The system according to any of Embodiments 18 and 19,wherein the emissions control software is configured to select theimproved shape responsive to detecting the improved shape minimizes EMEwith respect to other shapes of the reference signal.

Embodiment 21: The system according to any of Embodiments 18 through 20,wherein the touch sensing system is configured to store the improvedshape for the reference signal.

Embodiment 22: The system according to any of Embodiments 18 through 21,wherein the one or more emissions requirements comprise emissionsrequirements defined by a standard.

Embodiment 23: The system according to any of Embodiments 18 through 22,wherein the one or more emissions requirements comprise emissionsrequirements defined by customer requirements.

Embodiment 24: The system according to any of Embodiments 18 through 23,further comprising an emissions measurement equipment configured toprovide EME measurements responsive to EME exhibited by the touchsensor.

Embodiment 25: A method of configuring a touch sensing system to controlfor electromagnetic radiation (EME), the method comprising: providingreference signals for sensing operation, each of the reference signalshaving a different shape; detecting an improved shape for a referencesignal responsive to measurements indicative of electromagneticradiation (EME) emitted by a touch sensor during the sensing operations;and storing instructions for generating the reference signal having theoptimal shape.

Embodiment 26: The method according to Embodiment 25, wherein theproviding the reference signals during the sensing operation comprises:providing a first reference signal during a first sensing operation, thefirst reference signal having a pre-selected shape; receiving first EMEmeasurements during the first sensing operation; determining that thefirst EME measurements is greater than an emissions requirement;providing a second reference signal during a second sensing operation,the second reference signal having a second shape; receiving second EMEmeasurements during the second sensing operation; and determining thatthe second EME measurements are less than the emissions requirement.

Embodiment 27: The method according to any of Embodiments 25 and 26,further comprising selecting one of the first and the second shapes thatcorresponds to a lesser of the first and the second EME measurements.

Embodiment 28: The method according to any of Embodiments 25 through 27,further comprising: detecting that the first EME measurements are notless than the emissions requirements; determining changes to the firstshape that might affect EME emitted by the touch sensor during a sensingoperation; and selecting a sequence of n-bit codes corresponding to thesecond shape responsive to the determined changes.

Embodiment 29: The method according to any of Embodiments 25 through 28,wherein the selecting the sequence of n-bit codes corresponding to thesecond shape comprises selecting at least some n-bit codes of thesequence of n-bit codes that correspond to the determined changes to thefirst shape.

Embodiment 30: The method according to any of Embodiments 25 through 29,wherein the selecting at least some n-bit codes comprises selecting atleast some n-bit codes that correspond to non-monotonic portions of thesequence of n-bit codes.

What is claimed is:
 1. A method, comprising: selecting a first code of anumber of stored codes, each of the number of stored codes for arespective waveform shape for a digital-to-analog converter (DAC);providing the first code, wherein the first code for a first waveformshape is associated with a first sampling rate; providing a first shapedreference signal for a touch-sensor driver responsive to the first codefor the first waveform shape; generating a drive signal for a touchsensor responsive to the first shaped reference signal; and reporting atouch responsive to a changed signal level of the drive signal.
 2. Themethod of claim 1, comprising: outputting the first code for the firstwaveform shape responsive to a first fundamental frequency, wherein thefirst fundamental frequency is associated with a first sampling rate;and outputting a second code for a second waveform shape responsive to asecond fundamental frequency, wherein the second fundamental frequencyis associated with a second sampling rate.
 3. The method of claim 2,comprising: provide a first bit stream based, at least in part, on afirst sequence of n-bit codes corresponding to a shape of the firstshaped reference signal; and provide a second bit stream based, at leastin part, on a second sequence of n-bit codes corresponding to a shape ofa second shaped reference signal.
 4. The method of claim 3, comprising:providing the first bit stream at a first rate associated with the firstsampling rate; and providing the second bit stream at a second rateassociated with a second sampling rate.
 5. The method of claim 1,comprising: measuring at the touch sensor at the first sampling rate;determining interference responsive to the measurement at the touchsensor; and determining a second sampling rate.
 6. The method of claim5, comprising: providing a second code for a second waveform shapeassociated with the second sampling rate; providing a second shapedreference signal for the touch-sensor driver responsive to the secondcode for the second waveform shape; and generating a second drive signalfor the touch sensor responsive to the second shaped reference signal.7. The method of claim 5, wherein determining the second sampling ratecomprises determining the second sampling rate to reduce asusceptibility to foreign noise.
 8. The method of claim 1, comprising:determining that a sampling rate of the touch sensor has changed fromthe first sampling rate to a second sampling rate; providing a secondcode for a second waveform shape associated with the second samplingrate; providing a second shaped reference signal for the touch-sensordriver responsive to the second code for the second waveform shape; andgenerating a second drive signal for the touch sensor responsive to thesecond shaped reference signal.
 9. A method, comprising: selecting afirst code of a number of stored codes, each of the number of storedcodes to generate respective waveform shapes via a digital-to-analogconverter (DAC); providing the first code, wherein the first code for afirst waveform shape is associated with a first fundamental frequency;providing a first shaped reference signal for a touch-sensor driverresponsive to the first code for the first waveform shape; generating adrive signal for a touch sensor responsive to the first shaped referencesignal; and reporting a touch responsive to a changed signal level ofthe drive signal.
 10. The method of claim 9, wherein selecting the firstcode is responsive to qualitative electromagnetic emissions (EME)information characterizing an associations of the first fundamentalfrequency and the first code.
 11. The method of claim 10, wherein thequalitative EME information comprises a first characterization ofharmonics of the first fundamental frequency and the first code.
 12. Themethod of claim 9, comprising: measuring at the touch sensor at a firstsampling rate; determining interference responsive to the measurement atthe touch sensor; and determining a second fundamental frequency. 13.The method of claim 12, comprising: providing a second code for a secondwaveform shape associated with the second fundamental frequency;providing a second shaped reference signal for the touch-sensor driverresponsive to the second code for the second waveform shape; andgenerating a second drive signal for the touch sensor responsive to thesecond shaped reference signal.
 14. The method of claim 13 whereindetermining the second fundamental frequency comprises determining asecond sampling rate to reduce a susceptibility to foreign noise anddetermining the second fundamental frequency responsive to the secondsampling rate.
 15. The method of claim 9, comprising: determining that asampling rate of the touch sensor has changed from a first sampling rateto a second sampling rate; determining a second fundamental frequencyassociated with the second sampling rate; providing a second code for asecond waveform shape associated with the second fundamental frequency;providing a second shaped reference signal for the touch-sensor driverresponsive to the second code for the second waveform shape; andgenerating a second drive signal for the touch sensor responsive to thesecond shaped reference signal.
 16. A method, comprising: providing acode for a waveform shape for a digital-to-analog converter (DAC),wherein the code for the waveform shape is associated with exhibitingelectromagnetic emissions (EME) at a touch sensing system below a limitand wherein the waveform shape has been tuned to include a rising edgehaving one or more non-monotonic portions, a substantially flat topedge, and a falling edge having one or more non-monotonic portions;providing a first shaped reference signal for a touch-sensor driverresponsive to the code for the waveform shape; generating a drive signalfor a touch sensor responsive to the first shaped reference signal; andreporting a touch responsive to a changed signal level of the drivesignal.
 17. The method of claim 16, wherein the rising edge comprisestwo or more steps exhibiting successively increasing amplitude andwherein the one or more non-monotonic portions include one or more stepsexhibiting a lower amplitude than a preceding step.
 18. The method ofclaim 16, wherein the falling edge comprises two or more stepsexhibiting successively decreasing amplitude and wherein the one or morenon-monotonic portions include one or more steps exhibiting a higheramplitude than a preceding step.
 19. The method of claim 16, comprisingselecting the code from among a number of codes for a number ofrespective waveform shapes.
 20. The method of claim 19, wherein each ofthe number of respective waveform shapes has been tuned to include arespective rising edge having one or more non-monotonic portions, arespective substantially flat top edge, and a respective falling edgehaving one or more non-monotonic portions.